Thermionic tube and circuit embodying the same



July 21, 1936.

F. S. M CULLOUGH THERMIONIC TUBE AND CIRCUIT EMSODYING THE SAME Filed April 18, 1929 INVENTOR Patented July 21, 1936 Wm RATENT-J orrleha THERMIONIC TUBE iAND KCIRCUIT EMEBQDXING THEiSAM Frederick. S.':MQg11l l9 l.lgh, Edgewood, Pa'., assignor to The Union Pittsburgh rs;

n tienar anger; Pittsburgh,

nlnlicatieh-ihreill ifi 92g, ;Sel'ial .;No. -355,089

' l ms-M h-2 9+);

This. invention r teslto. snaceldisclhar eldew vices-end more par i larly:L Q-lspac efii eh r e eyicespithe hot. .cathodettypelwhere n .a heater s s d fqr eat n cthe icathode heiinyehe 5 tion constitutes an improvement on ;the, tube 5.; hei rm f B fi ament g e -ele .p teh iel 5s; uhstenhel r eentire en thtthereetis sheepss bf. ube-hem ir t rh etesilee heeie.

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ievme e l hder heir llq l tlg ffilfl ll;o 'r tl lfizl 11? N81, therein a loose heater wire Tubes o f the l di; eetlr. heated e thede som q he e hlt e. ethe r; ieht eeeihet lemehtl il eeseh f the e 9 .ie hlef th Q ite; el hes hr e of, heating current to the oppos e ends of the filarnent, A tube of thelin dir as above described, .does n tial gradient along the cath that the heating current.

In certain types .of radiofapparatus itggis de sirablefto have a potentia l j gia equipotential .cathod e' charact' In my said application, the ,is sho wn way of, securing a potent'ia lfldrop betw end of the cylindrical cathode a'nd th end, but dueto the relatiyely ow the cathodematerial, this poten atively slight. The present inyent h tube of the indirectly heated cathogl type Wherein a substantial potential drop bet of the cathode and the other'gcan be vi and the amount of potential drgp can be ac rately determined in the'manu factu 're of the tube. In the accompanying drawing, I hav ejsho n diagrammatically one embodiment of my int/ en; tion. Figure 1 represents .schen' atically arnul tiple electrode tube andacircuitfor the same. Figure 2 is a similaryiew wherein a non equipotential cathode is provided "withou the use of a separate source of current inthe clqsed cathode circuit;

In the drawing, 2 -designates an enclosingen velope within whichis a cathode structure '3,-{a grid 4, and a cylindrical plate 5? i a The cathode structure -3 comprises a rod .6 -of insulating .material such as quar.tz, 5 arceramic composition or a. vitreous compositioni Embodiedflwithin ,therod mend xtend nal hrou ho or heater wire 1. Wrappedtightly abp t the rod, 6, preferably with the conv olu-j ens. relati e y elese to e her i e Wire 1 8 coil of wire 8 forms the cathode, and'it may b'e ee eewithh euhs ee rl hex s ne t e eihis wim e leh e t eeemnehhd e e Z' l' eart mete shew eem h ly; ee ierl he hh fi I o e en i e c i 8 ma be eehh e ledt r h a wire 9 with, a source of current; fl, lw'hil the ther ehQ it et ei i i h eted' e lr'he H Interposed between the grid 4 and the pla te fi ih rjetmey e r ded whet, at e t med a fqur th electrode I 2;,but which .is actually} an ex; eh iszhleh heg e hed d h ehrg t efe eh inthe patu of the grid. The wire ll, a n wn in the ,dr ng connects to the top o f thls' lfourth' electrode orii cathode extension l2. A w'ire '13 ees hgl, rem he our el e e ell e hee l e a high resistance M, and the other debt the big-h resistance connectsto the sour ei of ,cureh. 1! v v The provision oi the fourth electrode [2 islnot necessary, andjthe wire ll may connect directlytit The helater wire I may be energizedfrom any suitable sourcepf current, either direct orfalteijh I hav e indicated an alternating}trafis' fqriner zgas providing the vsource 6f CliiliGni: for lfi l i h? t e 'Thg: wire opwhic'h the helical cathode iii 1s fgrmed may have any desired resistance, a'jwire harms, t eleh e h: e etehee t i elmew ferred. By the term highresistancef? as herein used and as hereinafter used in the claims, I meant met ie eehdueteh e" th; r sssectional area and specific resistance o fjhwliich resh hi s e r due i a tube ,e ehrfi hli impar a t e ih s llh fii i l high impedance in order that'the current flow therethrough will be relatively small, but this'will.

be suiiicient to give apotential drop of a predetermined amount from one end of the coil 8 to the other. The coil will be heated by the conduction of heat through the refractory rod 6 from the heater wire 1, rather than by any heating effected from the source of current l0. By reason of the fact that the cathode 8 is in the form of a coil-, 3

itsresistance can be of any predetermined value, and can beof a veryappreciable value, whereas where the cathode is in the form of a metal cylinder, the resistance must necessarily berelatively low.

"fByf the provisionof the fourth electrode l2, 'and 'th'e' inclusion of this electrode in series with thecathode and source of current It], the'operat ing characteristics of the tube can be very accurately controlled, and a circuit and tube is provided which'is highly desirable'for some types of radiowork. j V r The; invention; therefore, provides a tube of the indirectly heated cathode type wherein an appreciable non-equipotential characteristic obtains in ,the cathode, and which further provides a tube whose'operation can be controlled in a. very'definite manner by the'provision of the fourth electrode in series with the cathode and the source of current It];

The provision of a-looped heater wire is preferable ,where the cathode is in the form of a coil, beea'use'the current flow in one side of the heater wire is opposed to the current-flow in the other side, and the'field set up by the current in one side of thewire'is neutralized by the field of the othenwith the result that no current is induced injithe cathode coil 8 which wouldset up an A. C.

ripple "or hum in the output circuit of the tube when the heater is energizing from a source of alternating current or from a source of pulsating direct current. v v The'arrangement shown in Figure 2 is substantially the same asthat shown in Figure 1 with the exception that the source of current I 0 is eliminated. In this'arrangement 25 designates theheater wire, 26 the, rod of insulating for're-- fractory material and 2l'is the helical cathode.

The cylindrical grid of the tube is designated amaze is a. cylindrical plate, While the cathode extension or fourth electrode 30 is interposed between the grid and the plate, this fourth electrode preferably being spaced relatively close to the plate, One end of the coiled or helical'cathode 21 is connected through the wire 3|- with the fourth electrode 30. 'I have adopted; in the drawing, the conventional schematic Y showing of the cylindrical elements. V e The wire of which the cathode is wound has a high resistance and the turns are relatively close together;

"jIn' the-operation of the tube there is of course a transfer of energyfrom'the cathode extension 'or jso called fourth electrode to the plate aswell as fr'omithe main body of the cathode to the plate. is'byreason of'the fact that both of these elements of the tubeare connected with the negative side of the source of plate voltage. This transfer of energy results in the setting up of'a current flow in the circuit comprising the high arrangement has the advantage over the ar- "rangement shown in Figure lin that the separate 'source ofldirect current voltage In is not required. The coil of insulated turns of wire constituting the cathode ofvthe tube constitutes also an iniductance'functioning as a choke coil which serves to eliminateor reduce variations in the output of the tube by reason of pulsations or alternations inthe current used in heating the cathode.

It will be understood that I have illustrated one embodiment of my invention and that various changes and modifications may be made therein and in the circuit in which the tube is adapted within the' contemplation of my invention and under the scope'of the following claims. v

claim; l .l l f l Ina thermionic tube having'an indirectly heated-cathode in the form of a helix, a grid and.

a plate, and a fourth electrode interposed between 7 the gridand the plate, a connection leading from one endof the helical cathode to thefsaid fourth electrode; and'means for connecting the other end of the helical cathodeand saidfourth elec- V trode externally of the tube.

2. In a thermionic 'tube having an indirectly heated cathode in the form of a coil of highresistance-wire, a grid, "a plate; a'fourth electrode interposed between the platefand thecathode, f said fourth electrode constituting in efiect an extension of' the cathode, and means for connecting the other end of the helical cathode and said fourth electrode externally of the-tube.

3. In a thermionic tube of the indirectly heated T cathode type wherein there is a cathodeheater 7 anda'helical cathode surrounding theiheater, said helical, cathode having the convolutions thereof'spaced from one another, a grid electrode,

a plate electrode and a fourth electrode adjacent the plateelectrode and between the grid'and the offcennected to one end of the helical cathode, all of saidjelectrodes being enclosed in an evacuated vessel; and means for connecting the other end of V plate', said fourth electrode having one end therethe helical cathode and said fourth electrode ex,-

heaterfl'ofa source of potential across the opposite endsfof thecathod'e, a high resistance being included in series between the source of current and one end of the cathode, I .f,

5. The combination with a thermionic tube of the indirectly heated cathode type wherein there is a cathode heater and ahelical cathodesurrounding the heater, of a source of potential connected across the opposite ends of the cathode, a high resistance being included in series between the source of currentand one endof the cathode,

mediate point of the high resistance.

6. In a thermionic tube, a heater wire; a helical the cathode through a'connection to an intersaid tube having-a plate circuit which connects to 9 cathode surrounding the heaterwire and out of 75 contact therewith, a grid surrounding the cathode, a plate surrounding the grid, a fourth electrode interposed between the grid and plate and connected to one end of said helical cathode, and means for connecting a source of electric current to the opposite end of said helical cathode.

7. In a thermionic tube, a heater wire, a helical cathode surrounding the heater wire and out of contact therewith, a grid surrounding the cathode, a plate surrounding the grid, and a fourth electrode interposed between the grid and plate and connected to one end of said helical cathode, and means for coupling a source of direct current in series with the helical cathode and said fourth electrode.

8. In a thermionic tube, a plate, a grid, a cathode in the form of a coil having the adjacent convolutions thereof spaced from one another, and a heater for energizing the coil, said coil constituting a choke for eliminating variations in the current flow between the plate and the cathode by reason of the use of alternating currents or pulsating currents in the heater, and means whereby a circuit may be completed across opposite ends of the coil.

9. In a thermionic tube having a plate, a grid and a heater, a choke coil surrounding the heater and constituting the cathode of the tube, and means whereby a circuit may be completed across opposite ends of the coil.

10. An electrode tube having a cathode in the form of an inductance, which cathode also has a high resistance as herein defined, a heater wire inside the cathode and arranged for heating the cathode, said cathode having an extension at one end thereof forming an electrode, which electrode is spaced outside the cathode, and a circuit to which the other end of said cathode is connected.

FREDERICK S. MCCULLOUGH. 

